1. Field of the Invention
This invention relates generally to an exposure control system for a photographic apparatus and more particularly to an improved exposure control system having a follow focus capability for a photographic apparatus of the type having means for initiating the energization of a source of artifical light to illuminate a photographic screen. The follow focus capability is made possible by an interceptor assembly which is automatically actuable in a simple and reliable manner upon receipt of a source of artificial light by the photographic apparatus.
2. Description of the Prior Art
The exposure system of a photographic camera when operated in conjunction with a flash or transient illumination is ordinarily adjusted as a function of the levels of illumination anticipated at the scene being photographed. An evaluation based on the anticipated level of illumination may be made based upon an application of the inverse square law of light energy propagation which may be additionally weighted to anticipate spurious room reflections. Under this law, the light energy available from a given source is considered to vary inversely with the square of the distance from that source. Accordingly to make an appropriate exposure mechanism adjustment for flash photography, source to subject distance is derived and the value of this distance is utilized to compute an appropriate exposure value or illuminational factor.
In some camera designs, exposure control adjustment for flash operation is effected automatically by incorporating within the camera apparatus what is termed as a follow focus system. With a follow focus arrangement, aperture adjustment or flash illumination output control is mechanically coupled with the range finding or focusing system of a camera. In effect, a follow focus control represents a second exposure control system for a camera. As such, its presence necessarily contributes to the size and complexity of a camera.
A follow focus control system for an exposure control system is described in a U.S. Patent entitled "Focus Responsive Exposure Control System" by V. K. Eloranta and E. K. Shenk, Ser. No. 3,750,543 filed Apr. 19, 1971 and assigned in common herewith. The patent describes a second flash mode control system wherein an electromagnetic device, such as a solenoid, is selectively maneuvered and energized to extend its plunger to arrest the position of exposure aperture blades in accordance with focal setting. A complete follow focus system is described in a U.S. Patent entitled "Apparatus and System for Flash Photography" by Lawrence M. Douglas filed Mar. 15, 1973 No. 3,832,722 and assigned in common herewith. This system achieves a requisite compactness to meet the overall camera design described in U.S. Pat. No. 3,714,879 and incorporates means for selective use of the follow focus system exclusively during the flash illuminated exposure mode of operation. The above follow focus system additionally provides a trim function to accomodate for slight variations in the sensitometric characteristic of the film as well as to insert a modicum of personal or overriding control over the automated system. The trim control has only one control element for operation in this manner substantially reducing the possibility that a camera operator may become confused or overlook a requirement for providing a trim control for that mode of operation for which he is currently using.
A follow focus system of the above described type is designed for operation in conjunction with a single lens reflex receiving system together with a motorized automatic film processing arrangement as described in U.S. Pat. No. 3,714,879, Supra. Exposure regulation within this thin, compact camera takes place as part of a complex multi-step program involving the conversion of an optical path between viewing and exposure operational modes. The follow focus system must therefore be selectively actuated within this complex program logic of the reflex camera when a flash unit is mounted thereon.
Photographic camera apparatus of the non single lens reflex type have also been provided with range responsive aperture adjustment (follow focus) as described in a U.S. Pat. No. 3,714,871 entitled "Camera Apparatus Adapted For Operation With Auxiliary Light Source" by R. J. Bresson, filed Sept. 13, 1971. Such follow focus systems automatically actuate to provide range responsive aperture adjustment upon the mounting of a flash unit and thus are not selectively actuated as part of a complex multi-step program involving the conversion between viewing and exposure modes.
It is therefore a primary object of this invention to provide an exposure control system with follow focus capability for a photographic camera apparatus wherein the follow focus system is automatically actuable in a single and reliable manner to provide a range responsive aperture adjustment upon the mounting of a flash unit upon the camera apparatus.
It is also an object of this invention to provide an exposure control system with automatically actuable follow focus capability for a photographic camera apparatus of the non single lens reflex viewing type.
It is an additional object of this invention to provide an exposure control system with follow focus capability for a photographic camera apparatus wherein a unitary biasing spring is strategically located to simultaneously perform a plurality of functions in order to simplify the mechanism for actuating the follow focus system upon the mounting of a flash unit upon the camera apparatus.
It is a further object of this invention to provide an exposure control system with follow focus capability for a photographic camera apparatus wherein the individual flash units need not be critically dimensioned in order to insure corresponding aperture adjustment between different flash units.
It is a still further object of this invention to provide an exposure control system with follow focus capability for a photographic camera apparatus including an actuating system responsive to the mounting of a flash unit on the camera for moving the follow focus system into its range responsive aperture defining position.
Other objects of the invention will in part be obvious and will in part appear hereinafter. The invention accordingly comprises the mechanism and system possessing the construction, combination of elements and arrangement of parts which are exemplified in the following detailed disclosure.